USA Trains SD40-2 LM-4S-G installation

[Gino]

Has anyone installed an LM-3S-G or LM-4S-G in an USA Trains SD40-2?
I loaded the new software per the instructions and tried to set the Full Load Current. The locomotive tries to set the current per the test but the current draw appears to be more than the PWR-56 can supply and sees the load as a short and shuts down. The test times out so the Full Load Current never gets set.
Has anyone come across this problem? If so is there a solution?
I have not seen this problem with other USA Trains 4 axle locomotives.

[gregeusa]

The gearing is a bit different, and a little more friction driving the 3rd axle.

I'd try measuring the amps it draws on DC and see if something is abnormal.

even though the PWR56 is 4 amps, it is only 14.2 volts, really not appropriate for G scale, most G scale needs at least 18 volts, many G scale is 24v on the rails.

USAT motors have a very high stall current... for years the only decoder people would guarantee on USAT locos was the 8 amp NCE decoder.

So, see what it pulls on 14.2 volts... a cheap Harbor Freight meter will do the job.

Greg

[Gino]

I measured the current draw using a Chicago Model International 40MS DC power pack.
At full speed with the locomotive on the track and the wheels spinning the current draw was approximately 3.6 amps in one direction and approximately 3.2 amps in the other direction.
Track voltage is approximately 14.8V.
This is an older locomotive I purchased used so I am not sure the conditions of the motors. If there is info on what the typical current draw should be that would be nice to find out.

Appreciating the response.

[gregeusa]

So you are very close to the rated current for the PWR56, and note that your meter is undoubtedly averaging the reading, so peaks could easily exceed the 4 amp rating of the PWR56.

I would suggest trying a higher current supply, but then of course you are also reaching the limit of the decoder itself.

Greg

[Gino]

Greg,
Thanks for responding.

The PWR-56 comes with a PA-2 Brick power supply
So if I am clear on what you are saying you could replace the PA-2 with a Brick power supply with a higher current rating.
This would make sense but will this be a problem for the PWR-56?

Another option, since G Scale uses a higher voltage, would be using a Brick or filtered power supply with a higher voltage, say 18 volts and higher current rating. Again would this be a problem exceeding the input requirements for the PWR-56?

[gregeusa]

I have no idea what the input limits of the PWR-56 are.

I am NOT recommending changing the power supply to it, I will defer to RailPro on what you can give to it.

Remember (and someone correct me if I am wrong), the PWR-56 supplies power to the rails AND it functions as a repeater (this is a mesh network).

So I would say you power the rails with higher voltage and current AS LONG AS the setting of max current function will work.

Again, it's not clear to me how that setting works... hopefully it is completely independent of the DC output of the PWR-56

Greg

[Gino]

Well the light just went on!

I just figured it out that the PA-2 is used to supply DC power to the rails and the PWR-56 is used as a repeater (and I am sue other stuff too). So in theory I could use an independent filtered DC power supply with a higher voltage and short circuit protection, not to exceed the input voltage of the LM-3S-G and LM-4S-G modules, to run the locomotives on the layout. I would use the PA-2 to power the PWR-56 as a repeater and all the other accessory modules.

My only concern is losing the short circuit feature. Not sure if the short circuit protection is only with the PA-2 or also part of the Radio System.

Have to do more research to confirm.

[Gibs]

First off you're at the wrong voltage, you need to be between 18V - 24/30V for the G scale LM3/4 respectively.

Since Volts and Amps are an inverse relationship for the given Wattage of a PSU, you need to up the voltage of  PSU to match you intended usage. Not until that's done will you be able to set a CORRECT MAX Amp draw.

As to what the Max voltage input for the PWR-56 is, I can't recall and I'm not at home to look it up for you.

[William Brillinger]

The PWR-56 is not intended for use with G scale modules. You need to provide power from a separate power supply that is in the correct ranges.

[gregeusa]

We all agree about the higher voltage to the loco.

But is there any specification as to the max input voltage of the PWR-56?

For some G scale installations lower than 24 volts will be fine.

It is NOT necessary to supply power to match the MAXIMUM ratings of the LM-4S-G, what is needed here is to match the current and voltage requirements of the USA Trains loco (as long as the rest of the system can handle it).

If you were running only small LGB steam locos, where the prototype rarely went over 35 miles per hour, the PWR-56 might be fine.

Greg

[Gino]

I asked RailPro what to do and here is what they said/suggested:

"We may offer a higher power supply for G scale at some point.

You can parallel (tie + outputs together and to one rail of track and tie - outputs together and to the other rail of track) two PWR-56 to supplies for more power.  Warning: You should never connect any more than the two PWR-56 to a layout if you do this. 

If you are using only LM-4S-G modules you may want to use a USA Trains 10 amp power supply.  We have tested LM-4S-G on USA trains 10A power supply and it works ok with the power supply we tested.  The PWR-56 is 4 amps.  So the 10A power supply has more than twice the power of our PWR-56." 

I am not comfortable tying two PWR-56's together for higher current.

So I have another question. If a USA Trains 10 amp power supply has been tested and works with the LM-4S-G why not use a suitable fixed DC Power Supply to do the same job?

My understanding is that the LM-3S-G has a maximum input voltage of 24V (28V for the LM-4S-G) per the spec sheet. From what I have read the USA Trains 10 A Power Supply has an output voltage of 20V.

Why not use a 20V 10A power supply to power the rails.
I have both LM-3S-G and LM-4S-G modules.

Gino

[William Brillinger]

"Why not use a 20V 10A power supply to power the rails."

There is no reason not to do this as long as you are not using any of the smaller HO decoders.

[Gino]

This is strictly a G Scale application.

Gino

[gregeusa]

According to the web site, a PWR-56 with the PA-2 power adapter is 14.2 volts, 4 amps.

Clearly it is a regulated supply.

Combining 2 in series would give you 28.4 volts at 4 amps.

According to the site, this voltage exceeds the maximum voltage of the decoder by 0.4 volts, but elsewhere the maximum voltage is listed as 30 volts. So, since they are regulated supplies, two PWR-56 (supplied by two PA-2)  should be fine for G scale up to 4 amps.

But now you have 2 repeaters close together, and there's no system architecture document about this.

Seems better to have your PWR-56 in the best "radio" / "repeater" location and use a different power supply to the rails.

But 20 volts might be a bit low for some G scale... I tested a 3 axle Aristo passenger diesel, and it only went 62 smph on 20v DCC, went 92-94 on 23.9v DCC...

So I would strive to get 24v on the rails for your G scale stuff, of course as Bill says, other RailPro decoders will not tolerate the higher voltages.

Greg

[zr1rob]

I have several Aristo SD45s running 4S (14.8V) batteries and LM-3S-G modules, and they run fine, but maxed at roughly 45mph. I also run an Accucraft GS4, and it has a 6S (22.2V) battery, but it doesnt do much better scale speed wise. It might depend on the motors in the model.